Method for producing a fine graphite cast iron



July 4, 1967 TAKEOMI OKUMOTO ETAL 3,329,495

METHOD FOR PRODUCING A FINE GRAPHITE CAST IRON Filed Oct. 17, 1965 Producing rare 0f eufecf/c graph/fa v 20 40 60 a0 Campos/Wow 0f ll lg-A/a/lay (Mg%) Fig 2 Emecf/c degree 67 Proabc/ng rate of eufecflc graph/re INVENTORS g q'fii OKumoUo cnr- 0K d BY l -sh'l'csugu m ebashk United States Patent 3,329,496 METHOD FOR PRODUCING A FINE GRAPHITE CAST IRON Takeorni Okumoto, Senri Okada, and Yoshitsugu Maebashi, Katsuta-shi, Japan, assignors to Hitachi, Ltd'., Tokyo, Japan, a corporation of Japan Filed Oct. 17 1963, Ser. No. 316,928 Claims priority, application Japan, Oct. 31, 1962, 37/47,519 3 Claims. (Cl. 75-130) This invention relates to a novel method for producing a fine graphite cast iron having little shrinkage and high wear resistance by adding an Al-Mg alloy to a molten 1ron.

It is well known that an eutectic graphite cast iron shows little shrinkage on solidification and exhibits a high resistance to wear when lubricated under low load conditions. It is also well known that the form of graphite in cast iron varies depending on the variation in the amount of oxygen contained therein. As the oxygen content decreases the graphite form changes in the following order: white iron, eutectic graphite, losette graphite, coarse flake graphite, losette graphite, eutectic graphite, fine particle graphite, super cooled white pig iron. Furthermore, it is known that an amount of sulfur present in a certain range gives a similar effect. Since the amounts of oxygen and sulfur at which the eutectic graphite is produced must be severely limited to a narrow range in a cast iron having the ordinary composition, it has been difiicult to produce a stable eutectic graphite.

It is a well known fact that a spheroidal graphite is produced by adding Mg (a deoxidizing and desulfurizing element) to molten iron. According to the present invention it has been found that when a minimum amount of Mg necessary for the spheroidization of graphite is added together with a suitable amount of A1, a stable eutectic fine graphite structure is formed. In the present process, separate additions of pure Mg and Al produces an undesirable low amount of eutectic graphite formed in the structure, whereas the addition of aluminum and magnesium as an alloy achieves a much better percentage of eutectic graphite formed in the structure. Thus the present invention resides in producing a stable eutectic graphite by adding a Mg-Al alloy containing 2060% by weight magnesium to molten iron having an eutectic degree of 0.7-1.1. Thus the weight percent alloy refers to the amount of magnesium present in the magnesium-aluminum alloy, the balance being essentially aluminum.

FIG. 1 is a curve which shows the relationship between the percentage of eutectic graphite formed in the structure, the amount of magnesium in the Mg-Al alloy and the amount of Mg present in the iron-alloy composition. For example, it shows the percentage of eutectic graphite structure formed in test pieces by adding to FC-20 standard molten iron (a cast iron defined in the Japanese Industrial Standards corresponding to ASTM, A48, Class 30B) from a cupola of 2060% by weight of a Mg-Al alloy and casting it in a sand mold, 40 x 40 x 40 mm. The resulting iron-alloy composition contained 0.05 to 0.5% by weight magnesium. As is readily apparent from FIG. 1, a remarkably excellent result is obtained by the addition of 30% by weight of a Mg-Al alloy to molten iron such that the final iron-alloy composition contained 0.1% magnesium.

FIG. 2 is a curve which shows the relationship between the percentage of a fine eutectic graphite structure and the eutectic degree of the molten iron when 30% by weight of a Mg-Al alloy is added to produce an ironalloy composition containing 0.1% by weight magnesium. That is, it shows the percentage of the eutectic graphite formed in test pieces produced by adding 30% of a Mg-Al alloy, to the molten iron to produce a composition containing 0.1% magnesium. The eutectic degree of molten iron is adjusted to 0.7l.1 keeping the Si content at the 2% level constant, by adding steel scrap, ferro-silicon or electrode graphite to FC-ZO grade iron and casting the molten iron as mentioned on the FIG. 1. FIG. 2 shows that a high percentage of the eutectic graphite is formed according to the process of the present invention which is substantially independent of the eutectic degree (Sc). The fluidity of the molten iron treated according to this invention can be lowered, and if necessary, up to 1.0% by weight of one or more of P, Se, Te and rare earth elements may be added to the molten iron after the treatment with the Al-Mg alloy. The addition of phosphorus results in the formation of stedite (eutectic ferrite and Fe P) and in the enhancement of wear resistance of the cast iron product. Since the addition of aluminum-magnesium alloy sometimes causes the incorporation of dross and the formation of pinholes, the presences of selenium and tellurium are effective in preventing such occurrences. Rare earth elements prevent the reduction of the amount of eutectic graphite when a thick cast iron product is produced.

Above are the explanations of this invention. In short, this invention is characterized in that it comprises adding 20-60% by weight of a Mg-Al alloy to molten iron having an eutectic degree of 0.7-1.1. Less than 20% by Weight of Mg in the alloy is not desirable because the percentage of the eutectic graphite will become suddenly lowered as a result. More than 60% of Mg is also undesirable because of high explosiveness and low yield regarding the additives. The reasons for restricting the eutectic degree to 0.7-1.1 are as follows: When the eutectic degree is less than 0.7, the chilling tendency of the iron increases and it becomes difficult to produce good gray cast iron. When the eutectic degree is more than 1.1, kish graphites are produced rather than the fine graphites of the present invention.

The eutectic degree (So) as defined in FIGURE 2 can also be called the degree of saturation as disclosed in W.- Hiller and Walkling, Foundry, vol. (December 1962), page 54, and can be represented by the equation:

Percent O or Percent C Sc= 1 l 4.3 (SH-percent P) 4=.23 (percent Si) Also, eutectic degree is directly related to carbon equivalent which can be represented by the equation:

CE=percent C+ /3 (percent Si-l-percent P) 3 by weight of the iron composition, and casting said com position in a sand mold.

2. The process of claim 1, wherein said magnesium is present in the alloy in an amount of about 30% and in the iron composition in an amount of about 0.1% by weight.

3. A process for producing fine eutectic graphite iron which consists essentially of adding to molten iron having an eutectic degree of about 0.7 to 1.1, a magnesiumaluminum alloy containing about 20 to 60% by weight magnesium, the balance being essentially aluminum, said magnesium representing about 0.05 to 0.5% by weight of the iron composition, and further adding up to about 1% by weight of a material selected from the group consisting of phosphorus, selenium, tellurium, the rare earth tion in a sand mold.

References Cited UNITED STATES PATENTS Millis et al. 75-130 Heine 75--130 Busby 75130- Wever et a1. 75-129 X Zifferer 75-130 Menzen 7558 Dickinson 75-130 X Osborn et al 75-130 DAVID L. RECK, Primary Examiner.

HYLAND BIZOT, Examiner. elements and mixtures thereof and casting said composi- 15 H W TARRING Assistant Examiner 

1. A PROCESS FOR PRODUCING FINE EUTECTIC GRAPHITE IRON WHICH CONSISTS ESSENTIALLY OF ADDING TO MOLTEN IRON A MAGNESIUM-ALUMINUM ALLOY CONTAINING ABOUT 20 TO 60% BY WEIGHT MAGNESIUM, THE BALANCE BEING ESSENTIALLY ALUMINUM, SAID MAGNESIUM REPRESENTING ABOUT 0.05 TO 0.5% BY WEIGHT OF THE IRON COMPOSITION, AND CASTING SAID COMPOSITION IN A SAND MOLD. 